Added

• The nrfutil sdk-manager sdk install subcommand now prints a warning after a successful install to inform the user that the SDK installation needs to be registered with cmake.
• Added nrfutil sdk-manager sdk register <version> subcommand which registers the specified SDK with cmake using the SDK's corresponding toolchain. The toolchain version can be overridden with --toolchain-ncs-version or --toolchain-bundle-id flags.